As an admin user you can:
Add and edit users
Administrate groups
Downgrade and upgrade client companies.
Reset client data (Settings - Reset data)
The group All clients contains all client companies in that accounting office.
You can change a users access level to this group from user or group administration.
A group that is created will by default not have access to any clients. You can add client companies to the group from the client search box in the Clients tab.
You can also give a user access to a group from the menu User administration.